1. Field of the Art
The present invention relates to a process for the preparation of olefin polymers. More particularly, the present invention relates to a process for the polymerization of .alpha.-olefins having at least 3 carbon atoms, in which a polymer having a high stereoregularity is prepared in a high yield by using a catalyst which does not contain an electron donor such as an organic acid ester, an amide or an ether as an internal donor or external donor.
2. Description of the Prior Art
It is said that a catalyst system comprising a solid catalyst component having a titanium compound supported on a magnesium halide and an organoaluminum compound has a higher polymerization activity than conventional catalyst systems, and removal of the catalyst residue from the polymer formed is not necessary. However, the stereoregularity of the polymer formed by using this supported type catalyst is low, and it has been considered that omission of the step of extracting an atactic polymer is not permissible. Recently, various catalyst systems in which the stereoregularity is considerably improved by using a solid catalyst component comprising a magnesium halide, a titanium compound and an electron donor, especially a specific carboxylic acid ester, have been proposed (see Japanese Patent Publications No. 52-36786, No. 52-36913 and No. 52-50037).
According to these proposals, in order to obtain a polymer having an industrially appreciable high stereoregularity, it is ordinarily necessary to use an electron donor component, especially a specific carboxylic acid ester, in addition to a solid catalyst component and an organoaluminum compound. As a result, the obtained polymer has involved a serious problem of generation of a smell owing to the catalyst residue derived from the solid catalyst component and the electron donor component used at the polymerization. It is very difficult to eliminate the smell-generating cause in the polymer by a post treatment, and such a post treatment is disadvantageous from the industrial viewpoint.
Generally, in the step of preparing a solid catalyst component having a high activity and providing a polymer having a high stereoregularity and good properties, which contains an electron donor such as an ester, it is necessary to perform a heat treatment by using a large amount of TiCl.sub.4. Accordingly, recovery and disposal of TiCl.sub.4 after the use are necessary, and the catalyst-preparing apparatus and operation become complicated. Therefore, improvement of the technique of preparing the solid catalyst component has been desired
Furthermore, a method in which a magnesium halide is contacted with TiCl.sub.4 and an electron donor component by pulverization, followed by washing with a solvent such as a halogenated hydrocarbon compound, if necessary has been proposed. In this method the heating step using a large amount of TiCl.sub.4 is not indispensable. However, the properties of the polymer obtained are inadequate, and further improvement is desired. The polymer properties are very important in slurry polymerization and gaseous phase polymerization. For example, if the polymer properties are poor, such troubles as adhesion of the polymer in a polymerization vessel and insufficient withdrawal of the polymer from the polymerization vessel arise. Furthermore, the polymer concentration in the polymerization vessel has a close relation to the polymer properties, and if the polymer properties are poor, it is impossible to increase the polymer concentration in the polymerization vessel. The fact that it is impossible to increase the polymer concentration is very disadvantageous from the industrial viewpoint.
A process for preparing a solid catalyst component for the polymerization of olefins, which does not comprise an electron donor such as a carboxylic acid ester, is proposed in, for example, Japanese Patent Application Laid-Open Specifications No. 54-78786, No. 58-5309, No. 58-5310, and No 58-5311. According to these proposals, polymerization of an .alpha.-olefin having at least 3 carbon atoms is carried out in the presence of a catalyst system utilizing a carboxylic acid ester as an external donor. Accordingly, the stereoregularity and yield of the formed polymer are very low.
A process in which a solid catalyst component, an organoaluminum compound component and an organic silicon compound component having an Si--O--C linkage are used for polymerizing an .alpha.-olefin having at least 3 carbon atoms is proposed in Japanese Patent Application Laid-Open Specifications No. 54-94590 and No. 55-36203, Japanese Patent Publication No. 58-21921 and Japanese Patent Application Laid-Open Specification No. 57-63310. However, in these proposals, a heat treatment using a large amount of TiCl.sub.4 is necessary or the properties of the obtained polymer are inadequate, and further improvement is desired.
A process in which an .alpha.-olefin having at least 3 carbon atoms is polymerized by using a solid catalyst component free of an electron donor such as a carboxylic acid ester, an organic aluminum compound component and an organic silicon compound having an Si--O--C linkage is disclosed in Japanese Patent Application Laid-Open Specifications No. 56-41206 and 57-63312. However, these processes are inadequate for obtaining satisfactory stereoregularity, activity and polymer properties, and the above mentioned technical problems cannot be solved according to these processes.